The present exemplary embodiments relate to printing systems and, in particular, printing devices which utilize a supply of colored inks to be communicated to a print head for document printing. More particularly, the present embodiments utilize solid ink sticks as the supply ink, which must be heated to a liquid form before being capable of communication to the print head. Such systems are commercially available under the PHASER® mark from Xerox Corporation.
The present embodiments concern the structure, control system and operation methods of the heater element for causing a phase change in the solid ink supply to a liquid form capable of fluid communication to a print head for document printing.
The basic operation of such phasing print systems comprises the melting of a solid ink stick, its communication to a reservoir for interim storage, and then a supply process from the reservoir to a print head for printing of a document. One object of the control strategy is to avoid the printing system running out of ink while trying to print, because such an event can be a catastrophic failure to the system. Prior known systems will typically supply a measuring device in the reservoir to monitor ink levels therein. When the ink drops below a certain level due to normal usage, then the ink supply control system would melt more of the solid ink supply until the reservoir would refill to the desired level. The steps of asking for more ink, turning on the heater to melt the solid ink, delivering the ink to the reservoir to a desired level and then turning the heater off is commonly referred to as an “ink melt duty cycle.”
Conventional systems used a fixed applied power supply to the heater that was intended to provide a desired melt rate for the ink into a reservoir that was relatively large (approximately twenty-two grams of ink could be held therein). The ink level detector would initiate an ink melt duty cycle when the measuring device indicated that the ink level had dropped below a predetermined level. In the situation where an ink stick jam has occurred, i.e., the solid ink stick is obstructed from sliding down the ink loader tray to engagement with the heater, the continued supply of energy to the heater would not be able to melt the solid ink stick, because the stick was spaced from the heater itself. If the reservoir were to actually run dry, the printing system would suffer a catastrophic failure and would be unable to print. In addition, the continued application of the power to the elements of the heater could cause high temperature damage to the heater itself and to adjacent componentary. The print head could become clogged requiring an expensive maintenance repair with significant printer down time.
In order to avoid the possibility of running out of ink after it had dropped below a certain level in the reservoir, conventional systems employed a timer which would time out after a preselected amount of time that was assumed would not be enough time to let the reservoir run out, even for maximum printing usage of that color. If the measuring device did not indicate a refill of the reservoir during the time out period, the controller would disable the application of energy to the heater, thus assuming an ink stick jam. The system would disable further printing and heating after the elapse of the timer time-out cycle. This time out was calculated as the number of seconds of usable ink remaining in the reservoir based on the print image and mode that uses the maximum amount of ink. After the time out, the software would disallow printing until the ink level in the reservoir increased and was sensed by the ink level sense probe. Since the time out is based on the maximum possible ink usage, the printer was frequently not allowed to print which caused the printing rate to fall below specifications. Lastly, after the time out, the ink stick jam could then be identified and corrected, and the reservoir would then have to be refilled before printing could recommence.
The present exemplary embodiments are intended to employ a smaller reservoir of approximately five to six grams of ink. Smaller reservoirs present an advantage of not having to heat larger ink portions to remain liquid in the print head. In a maximum fill printing operation, the smaller reservoirs can be drained relatively quickly so that a time-out operation before assessing an ink stick jam presents an unacceptable risk of a reservoir going dry and consequential damage to the print head and the jets therein. There is a need for a system which can provide a more accurate indication of an ink stick jam to provide for improved operating control of system operation and improved safety against a catastrophic failure of a dried out reservoir occurring during a print operation. There is also a need for more efficiency in controlling the melt duty cycle to improve the overall printing rate. The present exemplary embodiments satisfy these needs as well as others to provide an improved method and assembly for detecting an ink stick jam in a phasing printing system. However, it is to be appreciated that the present exemplary embodiments are also amenable to other like applications where the supply of power to the heating element needs to be interrupted relatively soon due to the failure to supply an item intended to be heated by the heater element.